Pressurized writing instruments have been in use for many years. Pressurized devices were incorporated into writing instruments to improve and maintain continuous ink flow to the tips of the writing instruments during operation of the instruments for extended periods in horizontal and upside down positions. Moreover, the use of pressurized devices in writing instruments has reduced the need to vigorously shake the instrument to initiate ink flow after mere storage of a partly empty pen or cartridge in an inverted position.
Pressurized systems have been used to minimize solvent loss in writing instruments which employ highly volatile solvents and in applications which employ high viscosity inks wherein pressure is needed to force the flow of ink to the writing tip.
Mechanical and chemical pressurizing devices are two types of pressurizing systems which have been employed in writing instruments. Mechanical pressurizing devices contain a mechanism such as a spring to maintain constant pressure on the writing medium as consumption of the writing medium proceeds. Gas pressurized systems produce a pressurized gas such as nitrogen through chemical reactions, fermentation and the like, to maintain pressure on the writing medium for continuous supply of the medium to the point or nib of the writing instrument.
U.S. Pat. No. 3,130,711 to Eckerle discloses a positive pressure ball point pen which employs a gas pressurized system to maintain pressure on the writing medium in the pen. Pressure is maintained as the result of an electrolytic action between dissimilar metals (metals having different positions in the electromotive series of metals) within the pen or cartridge. The container body or cartridge is formed of a metal such as brass and portions of the inner surface thereof are coated with a different metal such as zinc. The zinc layer is coated with an insulative protective layer which is insoluble in the writing medium (ink) but soluble in the hydrocarbon grease plug which acts as an ink follower. A body of fluid electrolyte is disposed behind the hydrocarbon grease plug and contacts the dissimilar electrode metals as the ink becomes depleted. A gas is produced as the metals come into contact with the electrolyte. Hence, the pressure is maintained as the ink is consumed. A rubber plug is inserted into the end of the container to seal the system from the outside atmosphere and prevent leakage thereof.
Although plug members as described above are used in gas pressurized systems to maintain a seal on the writing instrument and prevent leakage of the gas from the system, poor seals often result from the inability to hermetically seal a plug within the writing instrument. This is difficult to do in gas pressurized systems which prevent the use of certain bonding techniques due to the potential interaction or exposure of the bonding material or solvent with the gas. In an effort to provide more effective sealing, liquid sealants have been used in conjunction with plug members to maintain the integrity of the gas seal. This combination often produces internal pressure variations which interfere with the uniform flow of the writing medium.
There remains a need for a writing device in which the internal pressure is maintained throughout the entire life of the writing device without overly complex or expensive seals to allow for smooth and continuous flow of ink regardless of the orientation of the writing device. It is desirable to provide a gas pressurized writing device having a tight seal whereby gas is not lost to the atmosphere.